The present disclosure relates generally to an engine coolant pump drive system and apparatus, and particularly to a variable speed engine coolant pump drive system and apparatus.
A typical engine cooling system employs an engine driven water pump, driven by a belt for example, for circulating coolant fluid, such as a water-glycol mixture for example, that is circulated through the engine block and the radiator. Since the pump is driven directly by the engine using a belt, its speed is determined by that of the engine, and it operates continuously as long as the engine is running, resulting in continuous losses due to constant operation and constant circulation of the coolant fluid through the cooling loop, whether the cooling action is needed or not. Also, the pump has to be designed to provide the required flow and pressure for the worst-case engine speed, which could be near idle or during high grade towing. This results in much higher pump flow at higher engine speeds than is necessary, further increasing the losses in the coolant system, which results ultimately in increased fuel consumption.
Other water pump systems have been introduced to decouple the coolant pump from the engine and provide an on-demand coolant flow using an electric motor-driven or electrically operated clutch driven pump. Both of these systems offer improvement to the vehicle fuel economy by providing an on-demand coolant flow and minimizing and/or eliminating the parasitic losses associated with the engine belt-driven coolant pump. However, the electric motor-driven coolant pump needs a high power electric motor, power electronics for controlling the speed of the motor, and a reliable electrical power supply, which includes the engine driven alternator and the battery. The overall power losses in a typical electric motor-driven coolant pump still involves significant losses through the engine alternator, power electronics, electric motor, and pump system. An electrically operated clutch driven coolant pump, employing an electromagnetic clutch for example, may be either on or off, with no continuous adjustment of the output speed being possible, resulting in significant shock loads on the engine.
Accordingly, there is a need in the art for an engine coolant pump drive system that overcomes these drawbacks.